Swapping them is pretty easy. Insert a 5mm Allen key into the left side of the axle. Insert a 5mm Allen key into the right side of the axle. Turn the right side Allen counterclockwise until it completely unscrews. This can be done with the cassette on or off the freehub body. Pull off the current freehub. Insert the new. If you think the axle needs a little grease, go ahead and put a little on. Reynolds uses Super Lube, but you can use whatever. When the new body is pushed fully on, get that right side nut, place it atop the threaded axle end, and with with your 5mm hex keyWant to turn clockwise until it is snug. If your freehub body arrives with an extra rubber gasket, you can toss it. This piece is only needed if you have loose ball bearings- pretty much a thing of the past. The 11 speed Shimano/SRAM cassette includes new end caps so conversion from 10 speed does not require the wheel to be redished.

Will this fit a 10 speed cassette or just...

You can put a 10 speed cassette on it, but you will need to purchase an extra spacer to put behind the cassette (costs just a few dollars). See http://www.slowtwitch.com/Tech/Cassette_Spacers_2013_3978.html for a discussion of this and a chart that tells you which spacer(s) you will need (depends on the brand of cassette you have). You will also need to put a smaller end cap on (which came with my order), otherwise the wheel will not fit when you try to put it back on your bike (since the hub body is longer.

Have an answer for Chris?

End caps not included?!

Just got off the phone with Reynolds. I want to convert my 10 sp Reynolds Assaults to 11 speed. They say that in addition to this I'll also need two new end caps, which are another $20. With new caps, she said I shouldn't need to redish the rear wheel. They're sending me the package of parts I need for $95.

Can someone confirm if this freehub body ships with the cap needed to successfully convert to 11sp? Reynolds webstore says it includes the non drive side end cap (not needed on '13/'14 wheels) From above description: "The 11 speed Shimano/SRAM cassette includes new end caps so conversion from 10 speed does not require the wheel to be redished." this is from the description above and makes it sound like once I buy a cassette that it includes a end cap? whut?....is that a typo? (cassette should read freehub body, right?)